In case anyone is interested. I have been using remote battery operated sensors with the Moteino - Arduino with secure radio (cost $13). Connects to Rpi with a serial interface then on to HG via a MQTT message. (Using mosquitto software)
Works great and the sensor can have anything an Arduino hooks to: temp, humidity, light, motion etc.
Battery on the sensors, which are low power and last for > 1 year.
Here's the link to Moteino:
https://lowpowerlab.com/guide/moteino/The great thing about the Radio/Arduino is that it is NOT 2.4GHz so better range at lower Freq. and can be good distance at low Tx rates.